In U.S. Pat. No. 6,841,956, the description regarding FIG. 9 mentions that a platform intended for accommodating a wafer and supported in a manner allowing movement horizontally in the X- and Y-direction, is additionally adjustable by three single-phase motors (voice-coil motors) in a Z-direction, in order to permit exact positioning of the wafer in the Z-direction. The Z-direction is perpendicular to the platform and shall also be denoted here as direction of the normal. The three voice-coil motors all act in the same direction, thus, are able to adjust the platform at its respective point of force or application along the Z-direction.
European Patent No. 1 691 476 describes using a three-phase converter, actually intended to control a three-phase motor, to control a two-phase motor. Among other things, this has the advantage that, as frequently used standard modules, such three-phase converters are available particularly inexpensively.